1. Field of the invention
The present invention relates to a spread illumination apparatus for use of illuminating a signboard and various kind of reflection type of display, in particular, a liquid crystal display apparatus.
2. Related arts
As an auxiliary illuminating apparatus for illuminating the screen of a liquid crystal display apparatus an outlined constitution of a spread illumination apparatus (Japanese Patent Application No.Hei 10-345270) proposed by the inventors of the present invention is explained hereinafter while showing it in FIGS. 4 and 5. Further this spread illumination apparatus 1xe2x80x2 is indicated as a prior art. The spread illumination apparatus 1xe2x80x2 is used and disposed for covering the screen (front) F of a liquid crystal display element L, and comprises a transparent substrate 2 plane and sectionally rectangular made of a material having a high light permeability and a light source lamp 4 disposed at the one side end 3 of the transparent substrate 2. As the light source lamp 4, a bar-like one such as a cold cathode fluorescent lamp (CCFL) or a hot cathode fluorescent lamp (HCFL) is used. For reference, the transparent substrate 2 may happen to be wedge-like in configuration in order to become light-weighted.
Here, in FIG. 5, the surface of the transparent substrate 2 to be touched to the reflection type of liquid crystal display element L is to be called a lower surface 5 and its reverse surface is to be called an upper surface 6 (front surface) as an observation surface.
In FIG. 4, on the upper surface 6 of the transparent substrate 2, a light reflection pattern 7 is formed. The light reflection pattern 7 is formed along the one side end face 3 and formed of a plurality of grooves 8 approximately triangular and plane portions 9 adjacent to the grooves 8. The light reflection pattern 7 is adapted to be formed, regardless the distance from the light source lamp 4, in such a manner as, in order to realize an even and spread emission of the light from the transparent substrate 2, a spacing of the grooves to be formed is made different depending on the location of the groove. That is, the ratio of the area occupied by the groove to the area occupied by the plane portion is set in such a manner as it is increased gradually great as the grooves depart far from the one side end face 3 of the transparent substrate 2 where the light source lamp 4 is disposed nearby. Concretely, the width and depth of the groove or the spacing of the grooves to be provided may be varied.
And, on the sides of the light source lamp 4 and the transparent substrate 2 a reflection member 10 to reflect the light to the screen side is provided.
When disposing thus formed spread illumination apparatus 1xe2x80x2 so as to cover the upper surface of the reflection type of liquid crystal display element L, the emitted light from the light source lamp 4 enters the transparent substrate 2 from the one side end face 3 and progresses toward an opposite side 11 within it while repeating reflection and refraction. During which, since the light emitted from the lower surface 5 of the transparent substrate 2 illuminates the reflection type of liquid crystal display element L, the screen of the liquid crystal element can be illuminated bright.
At that time, since the light reflection pattern 7 is provided, the volume of the light emitted from the lower surface 5 is approximately even regardless the distance from the light source lamp 4, the reflection type of liquid crystal display element L can be illuminated in a spread manner.
On the other hand, since a spread illumination apparatus 1xe2x80x2 is formed with the light reflection pattern 7 consisting of the grooves 8 and plane portions 9 on the transparent substrate 2, there are following problems.
When producing actually the spread illumination apparatus 1xe2x80x2 having the above constitutions, disposing it in such a manner as it covers the observation face F of the liquid crystal display element L and observing the screen, it has been found that, nearby on the opposite surface 11, an image on the screen is observed in duplicate (hereinafter referred to as xe2x80x9cduplicate imagexe2x80x9d), which causes the quality of the picture to be degenerated outstandingly. For reference, since the grooves 8 of the light reflection pattern 7 formed on the transparent substrate 2 are quite fine, when observing the picture, these grooves can not be recognized by naked eyes.
The cause of generation of this duplicate image has been found to be caused by the grooves 8 of the light reflection pattern 7 of the transparent substrate 2. That is, as shown in FIG. 5, a picture of a picture element component Q comprises, in a fine level, a real picture passing through the plane portion shown in an arrow A and a phantom picture reflected by the grooves 8 shown in an arrow B (hereinafter referred to as xe2x80x9cduplicate image componentxe2x80x9d). Further, in the picture of picture element component Qxe2x80x2 comprises a real picture passing through the plane portion 9 shown in an arrow Axe2x80x2 and a duplicate image component shown in an arrow Bxe2x80x2. Accordingly, as shown in an area R, a duplicate image is generated due to overlapping of the real image (arrow Axe2x80x2) and a duplicate image component (arrow B). If the ratio of this duplicate image component is small, there is no problem because it is not recognized by naked eyes, if it is great, a duplicate image is observed. Since this duplicate image component is increased in proportion to the size of the occupied area (the width and the depth of the grooves 8), in other word, due to the pattern design of the light reflection pattern 7 formed on the transparent substrate 2 the duplicate image is observed more as close to the end portion 11 of the transparent substrate 2 (FIG. 4).
On the other hand, the light reflection pattern 7 is increased in brightness due to the increased volume of the light emitted from the upper surface 6 when the area occupied by the grooves 8 is increased.
As mentioned above, for avoiding the generation of duplicate image, it is preferable to reduce the occupied area of the grooves 8, on the other hand, for the purpose of increasing the brightness it is preferable to increase the occupied area of the grooves 8, therefore, so as to satisfy these contradictory conditions, the pattern of the light reflection pattern 7 has to be designed.
Accordingly, the purpose of the present invention is to provide a spread illumination apparatus to restrain the generation of the duplicate image while maintaining the brightness by restricting the occupied area of the grooves.
As a means to solve the above problems, according to a first aspect of the present invention, in a spread illumination apparatus of a side-light system, in which, nearby the side of the transparent substrate made of a material having a high light permeability, a bar-like (linear) light source is provided and a light reflection pattern is formed on the transparent substrate so as to equalize the volume of the emitted light spread on the screen, said light reflection pattern comprises a plurality of grooves formed along the bar-like light source and plane portions adjacent to such grooves, where the grooves are set slantwise at an angle in such a manner as the light to progress toward the grooves is emitted perpendicularly to the rear surface of the transparent substrate and, provided that a length from a groove to an adjacent groove is set as a pitch, the ratio of the width of the groove to the pitch is to be 0.01-0.15.
According to a second aspect of the present invention, said ratio is 0.01-0.1.
According to a third aspect of the present invention, said ratio of the width of the groove to the pitch is gradually increased from the side at which the bar-like light source is disposed to the opposite side thereof.
By structuring as mentioned above, in the spread illumination apparatus of the present invention, since the light reflection pattern formed with a plurality of grooves and plane portions adjacent to the grooves and the light to progress toward the grooves is emitted from the rear surface of the transparent substrate in such a manner as the angle of the groove is inclined so as to make the direction of the light to be emitted perpendicular to the rear surface, so that the light is introduced in a high efficiency, and that, by setting the ratio of the width of the groove to the pitch is set to the range of 0.01-0.15 (preferably 0.01-0.1), so that due to this restriction of the width and the depth of the groove, making the duplicate image to a duplicate image component to an extent where it is not recognized by naked eyes.